This invention relates to a coating process for applying a coating liquid to a substrate such as a glass substrate for a liquid crystal display (LCD), thereby forming a coating film such as a photoresist coating or an anti-reflective coating.
The LCD manufacturing process employs photolithography as the manufacturing process of a semiconductor device. In the photolithography for the LCD, a resist coating is formed on a glass substrate, and subjected to pattern exposure and then development. A semiconductor layer, an insulating layer and an electrode layer formed on the substrate are selectively etched, thereby forming an ITO (Indium Tin Oxide) thin film or electrode pattern, etc.
To coat the LCD substrate with a resist liquid, so-called spin coating is used. The spin coating is performed using a coating apparatus as disclosed in U.S. Pat. No. 5,688,322. In this coating apparatus, an LCD substrate is held by a spin chuck, a solvent and a resist liquid are dripped onto the substrate, and the spin chuck and a rotary cup are rotated in synchronism with each other, with the upper opening of the cup closed with a lid. Liquid drips or mist scattering from the substrate are received by a drain cup, thereby exhausting liquid components in the form of, for example, droplets to the outside of the cup through a plurality of liquid exhaust pipes, and gaseous components in the form of, for example, mist to the outside of the cup through a plurality of gas exhaust pipes.
Since each gas exhaust pipe opens to the periphery of the drain cup, that part of the mist which exists in the vicinity of the openings (exhaust ports) of the exhaust pipes is first exhausted, and thereafter the exhaust area gradually increases within the cup. Therefore, it is difficult to promptly exhaust the entire internal area of the cup.
The size of LCD substrates has recently increased from (650.times.550 mm) to (830.times.650 mm). If the substrate size more and more increases in near future, coating the substrate with a resist liquid will cause generation of a great amount of mist which may contaminate the resist coating. Since in particular, it is difficult to perform complete exhaustion after the rotation of the substrate is stopped, the resist coating is more likely to be contaminated by the mist. A great amount of mist is hard to sufficiently separate into a gas and a liquid in the drain cup, and hence a gas/liquid mixture will be exhausted through the gas exhaust pipes. This means that a great amount of mist will enter the gas exhaust pipes.